Video: Robotic Crabs Reveal Sexual Frustration in Crustaceans

With his huge, showy, yellow claw, the male Mjöberg’s fiddler crab (Uca mjoebergi) is an eye-catching crustacean that lives on the marine mud flats of northern Australia. Like many other fiddlers, he uses his claw to attract a mate, the much smaller and more demure female. Researchers have been studying how female fiddlers choose between their many suitors. They’ve learned, for instance, that males with larger claws, especially those that wave them faster, have an edge in dating. To amp up their science, however, they’ve added a robotic twist—building “RoboCrabs” that can wave an array of claws in a variety of ways. The automated fiddlers have helped the scientists uncover other factors that influence mate choice. In a study published this month in Behavioral Ecology, for example, they found that females showed a strong aversion to otherwise irresistible males if the guys were waving from the tops of small mounds. That might be because elevated mating sites are too dry or exposed to predators. But the researchers admit they aren’t sure why females scorned the elevated crabs—which they dubbed the “fiddlers on the roof.”